The instant message (IM) service is a kind of person-to-person or person-to-group message-type mobile data service based on the Presence and can be applied to mobile communication networks and the Internet. The mobile communication networks include current 2G network, 2.5 G network, future 3G network, IP Multimedia Subsystem (IMS) and the like.
Generally, there are two types of IM systems in the current industrial specifications. One is Wireless Village (WV) based, which is carried on Hyper Text Transport Protocol (HTTP)/Wireless Access Protocol (WAP)/Short Message Service Protocol (SMS) and supports 2.5G/3G network, and the other is SIP/SIMPLE based, which is carried on SIP/SIMPLE and supports IMS-based IP network.
In the IM system based on SIP/SIMPLE, it is desired that when a sender sends an instant message to a receiver who is offline, the IM server of the receiver selects whether it is necessary to store the deferred message according to user configuration and system configuration (i.e., whether the deferred message needs to be stored and retrieved and whether the function for supporting deferred message is provided, etc.). If the deferred message is stored, when the receiver registers to the SIP/IP core network and logs in the server of the receiver, the IM server can show the receiver a deferred message notification and if the receiver would like to obtain the details of one or more messages, the receiver may send a retrieving request to the server and then the server will issue the details of the selected messages to the receiver.